CODEWITHSUNDEEP
grayscalefreeimage24-bit
Bernhard
Bernhard

Reputation: 2809

freeimage convert png 24bit to 1bit black/white = grey/white?

I am using Freeimage.sf.net to load an png24bit and want to save it as black/white png. using

FIBITMAP bib = Freeimage.Load("<24bit_png>");

FIBITMAP conv = FreeImage.ConvertColorDepth(bib, FREE_IMAGE_COLOR_DEPTH. FICD_01_BPP_THRESHOLD, (byte) 128);

FreeImage.Unload(bin); bib.SetNull();

FreeImage.Save(FREE_IMAGE_FORMAT.FIF_PNG, conv, "<out_png>", FREE_IMAGE_SAVE_FLAGS.PNG_Z_BEST_COMPRESSION);

FreeImage.Unload(conv); conv.SetNull();

but the is not black/white, as it is #0b120c / white? why does the threshold not create a bw-palette?

Upvotes: 2

Views: 1363

Answers (1)

Sergey K.
Sergey K.

Reputation: 25396

The line

FIBITMAP conv = FreeImage.ConvertColorDepth( bib,
                   FREE_IMAGE_COLOR_DEPTH.FICD_01_BPP_THRESHOLD, (byte) 128 );

builds a palette for the most used colors.

Replacing it with

FIBITMAP bw = FreeImage.Threshold( biRef, threshold_BW );

will create a truly black-and-white image.

Upvotes: 1

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